Spinal fusion implant and related methods

ABSTRACT

The present invention relates generally to medical devices, systems, and methods for use in surgery. In particular, the disclosed system and methods relate to an intervertebral spinal implant sized and dimensioned for the lumbar spine implantable via a posterior approach. The system includes an implant, instruments for delivering the implant.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/597,085, filed on Jan. 14, 2015 (now U.S. Pat. No.9,730,802), which claims the benefit of priority from U.S. ProvisionalPatent Application Ser. No. 61/927,421, filed on Jan. 14, 2014, and U.S.Provisional Patent Application Ser. No. 62/009,647 filed on Jun. 9,2014, the entire contents of which are hereby expressly incorporated byreference into this disclosure as if set forth in their entirety herein.

FIELD

The present invention relates generally to spinal surgery and, moreparticularly, to a device for spinal fusion comprising a spinal fusionimplant of non-bone construction to be introduced into any variety ofspinal target sites.

BACKGROUND

Currently there nearly 500,000 spine fusion procedures performed eachyear in the United States. One of the causes of back pain and disabilityderives from the rupture or degeneration of one or more intervertebraldiscs in the spine. Surgical procedures are commonly performed tocorrect problems with displaced, damaged, or degenerated intervertebraldiscs due to trauma, disease, or aging. Generally, spinal fusionprocedures involve removing some or the all of the diseased or damageddisc, and inserting one or more intervertebral implants into theresulting disc space.

Minimally invasive methods of performing spinal fusion have gainedpopularity in recent years due to the many benefits of the procedurewhich include diminished dissection of body tissue and lower blood lossduring surgery resulting in reduced surgery time, lower post-operativepain and a quicker recovery for patients. Transforaminal lumbarinterbody fusion (TLIF) procedures provide unilateral access to adesired target site. The TLIF technique involves approaching the spinein a similar manner as a posterior approach but more from the left orright of the spine through a midline incision in a patient's back. Thisprocedure requires only one incision in the back of a patient andinvolves placing a fusion device into the intervertebral disc space.Introducing the intervertebral implant serves to restore the height(“disc height”) between adjacent vertebrae, which reduces if noteliminates neural impingement commonly associated with a damaged ordiseased disc.

SUMMARY OF THE INVENTION

The spinal fusion implant of the present invention may be comprised ofany suitable non-bone composition, including but not limited to polymercompositions (e.g. poly-ether-ether-ketone (PEEK) and/orpoly-ether-ketone-ketone (PEKK)), ceramic, metal, or any combination ofthese materials. The spinal fusion implant of the present invention maybe provided in any number of suitable shapes and sizes depending uponthe particular surgical procedure or need. The spinal fusion implant maybe dimensioned for use in any part of the spine (e.g. cervical, lumbarand/or thoracic) without departing from the scope of the presentinvention. The implant may be dimensioned, by way of example only,having a width ranging between 8 and 14 mm, a height ranging between 8and 18 mm, and a length ranging between 25 and 45 mm.

According to one broad aspect of the present invention, the spinalfusion implant includes a top surface, a bottom surface, lateral sides,a proximal end, and a distal end. The spinal fusion implant of thepresent invention may be used to provide temporary or permanent fixationalong an orthopedic target site. To do so, the spinal fusion implant maybe introduced into a disc space while locked to a surgical insertioninstrument and thereafter manipulated in the proper orientation andreleased. Once deposited in the disc space, the spinal fusion implant ofthe present invention effects fusion over time as the natural healingprocess integrates and binds the implant.

The spinal fusion implant of the present invention may be provided withany number of additional features for promoting fusion, such as one ormore apertures extending between the top and bottom surfaces which allowa boney bridge to form through the spinal fusion implant.

The spinal implant may also be preferably equipped with one or morelateral openings which facilitate visualization at the time ofimplantation and at subsequent clinical evaluations.

The spinal fusion implant may also be provided with any number ofsuitable anti-migration features to prevent the implant from migratingor moving from the disc space after implantation. Suitableanti-migration features may include, but are not necessarily limited to,angled teeth or ridges formed along the top and bottom surfaces of theimplant and/or rod elements disposed within the distal and/or proximalends.

The spinal fusion implant may be provided with one or more radiographicmarkers at the proximal and/or distal ends. These markers allow for amore detailed visualization of the implant during and after insertion(through radiography) and allow for a more accurate and effectiveplacement of the implant.

The proximal end of the spinal fusion implant may be provided with asurface that is tapered (angled) to avoid dural impingement afterimplantation. Additionally, the tapered nature of the proximal surfacecan aid in overall fit of the spinal fusion implant within theintervertebral disc space. Significantly, the tapered proximal surfaceon the proximal end enables the spinal fusion implant to maximizecontact with the posterior portion of the cortical ring of each adjacentvertebral body.

The distal end of the spinal fusion implant may be provided with aconical (bullet-shaped) shape including a pair of first tapered (angled)surfaces and a pair of second tapered (angled) surfaces. The firsttapered surfaces extend between the lateral surfaces and the distal endof the implant, and function to distract the vertebrae adjacent to thetarget intervertebral space during certain methods of insertion of thespinal fusion implant. The second tapered surfaces extend between thetop and bottom surfaces and the distal end of the spinal fusion implant,and function to maximize contact with the anterior portion of thecortical ring of each adjacent vertebral body. Furthermore, the secondtapered surfaces provide for a better fit with the contour of thevertebral body endplates, allowing for a more anterior positioning ofthe spinal fusion implant and thus advantageous utilization of thecortical rings of the vertebral bodies. The distal end of the spinalfusion implant may be at least partially asymmetrically curved about thelongitudinal axis to approximate the anterior portion of the corticalring of each adjacent vertebral body when the implant is placed in itsdesired final oblique position.

The spinal fusion implant may be provided with a variable height alongat least a portion of the implant. In one embodiment, the variableheight tapers in a direction oblique to both the length and width of theimplant. The oblique taper imparts a greater height to the anterioraspect of the intervertebral disc space when the spinal fusion implantis positioned obliquely within the disc space. Imparting a greaterheight to the anterior aspect of the disc space restores the naturallordotic curvature of the lumbar spine.

The spinal fusion implant may be provided with at least one set ofvariable opposing corner rounds varying in their radii along the lengthof the implant to allow for more gradual lead-in at the distal end whichfacilitates easier and safer insertion of the spinal fusion implant.

The spinal fusion implant may be further provided with asymmetric convextop and bottom surfaces between first and second lateral sides toapproximate the anatomical concavities of the inferior endplate of thesuperior vertebra and the superior endplate of the inferior vertebra.

The spinal fusion implant may be further provided with asymmetricallyconvex top and bottom surfaces along the length of the implant betweenproximal and distal ends of the implant. The asymmetric curvatureenables the spinal fusion implant to even better match the anatomicalconcavities of the inferior endplate of the superior vertebra and thesuperior endplate of the inferior vertebra.

The spinal fusion implant may be introduced into a spinal target sitethrough use of any of a variety of suitable surgical instruments havingthe capability to engage the implant. The spinal fusion implant iscapable of being used in minimally invasive surgical procedures, needingonly a relatively small operative corridor for insertion.

The spinal fusion implant may be inserted into the intervertebral spaceand rotated into final position. Once the implant has been positioned inits desired location within the intervertebral space, the user will thenrotate the implant 90° such that the top and bottom surfaces face in acaudad/cephalad direction and the anti-migration features engage thevertebral bodies. Significantly, the direction of rotation is criticalto ensure proper placement of the implant such that the edges of theproximal surface rest on the cortical ring of the vertebral bodies andthe proximal surface does not protrude into the spinal canal. Forexample, if the spinal fusion implant approaches a patient's spineposteriorly from the right with the (longer) first lateral side facingcaudally, then implant must be rotated in a counter-clockwise directionto achieve proper positioning.

A single spinal fusion implant may be provided and inserted into anintervertebral disc space and positioned obliquely across the disc spacesuch that the proximal and distal ends are on opposite sides of themidline of the intervertebral space.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of an example of a spinal fusion implantaccording to one embodiment of the present invention;

FIG. 2 is a second perspective view of the spinal fusion implant of FIG.1;

FIG. 3 is a top view of the spinal fusion implant of FIG. 1;

FIG. 4 is a bottom view of the spinal fusion implant of FIG. 1;

FIG. 5 is a first side view of the spinal fusion implant of FIG. 1;

FIG. 6 is a second side view of the spinal fusion implant of FIG. 1;

FIG. 7 is a plan view of a proximal end of the spinal fusion implant ofFIG. 1;

FIG. 8 is a detailed perspective view the proximal end of the spinalfusion implant of FIG. 1;

FIG. 9 is a detailed cross-section view of the proximal end of thespinal fusion implant of FIG. 1;

FIG. 10 is a plan view of a distal end of the spinal fusion implant ofFIG. 1;

FIG. 11 is a cross-section view of the proximal end of the spinal fusionimplant of FIG. 1 taken along the line 1-1;

FIG. 12 is a cross-section view of the distal end of the spinal fusionimplant of FIG. 1 taken along the line 2-2;

FIG. 13 is a perspective view of an insertion instrument according toone embodiment of the present invention;

FIG. 14 is an exploded perspective view of the insertion instrument ofFIG. 13;

FIG. 15 is a detailed perspective view of the distal end of theinsertion instrument of FIG. 13;

FIG. 16 is a perspective view of the insertion instrument of FIG. 13coupled to the spinal fusion implant of FIG. 1;

FIG. 17 is a perspective view of an implant trial instrument accordingto one embodiment of the present invention;

FIG. 18 is a side view of the distal head of the trial instrument ofFIG. 17 in a first orientation;

FIG. 19 is a side view of the distal head of the trial instrument ofFIG. 17 in a second orientation;

FIG. 20 is a side view of the distal head of the trial instrument ofFIG. 17 in a third orientation;

FIG. 21 A is a top plan view of an example of a spinal fusion implantinserted into an intervertebral disc space but not placed in a desiredoblique configuration;

FIG. 21 B is an example lateral x-ray indicating the position ofradiographic markers of the spinal fusion implant placed in theconfiguration shown in FIG. 21 A;

FIG. 22 A is a top plan view of an example of a spinal fusion implantinserted into an intervertebral disc space placed in a desired obliqueconfiguration; and

FIG. 22 B is an example of a lateral x-ray indicating the position ofradiographic markers of the spinal fusion implant in the desired obliqueconfiguration as shown FIG. 22 A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The spinal fusion implant, system, and methodsdisclosed herein boasts a variety of inventive features and componentsthat warrant patent protection, both individually and in combination.

FIGS. 1-2 illustrate a spinal fusion implant 10 according to a firstbroad aspect of the present invention. The spinal fusion implant 10 maybe constructed of any suitable non-bone composition, including but notlimited to polymer compositions (e. g. poly-ether-ether-ketone (PEEK)and/or poly-ether-ketone-ketone (PEKK)), ceramic, metal and/or anycombination of polymer compositions, ceramic and metal. The spinalfusion implant may be provided with a surface coating (for example,titanium plasma spray) to encourage bone growth onto endplate contactingsurfaces. The spinal fusion implant 10 of the present invention may beprovided in any number of shapes and sizes depending upon the particularsurgical procedure or need. By way of example only, the spinal fusionimplant 10 may have a width ranging between 8 and 14 mm, a heightranging between 6 and 18 mm, and a length ranging between 20 and 45 mm.

The spinal fusion implant 10 of the present invention includes a topsurface 12, a bottom surface 14, first and second lateral sides 16, 18,a proximal (posterior) end 20 and a distal (anterior) end 22. The spinalfusion implant 10 of the present invention may be used to providetemporary or permanent fixation within an orthopedic target site. To doso, the spinal fusion implant 10 may be introduced into a disc spacewhile locked to a surgical insertion instrument and thereafter employedin the proper orientation and released, as explained in further detailbelow. Once deposited in the disc space, the spinal fusion implant 10 ofthe present invention effects spinal fusion over time as the naturalhealing process integrates and binds the implant.

FIGS. 3-4 illustrate the top and bottom surfaces 12, 14, respectively,of the spinal fusion implant 10. The top and bottom surfaces 12, 14 areconfigured to engage the vertebral bodies adjoining the target discspace. Accordingly, the top and bottom surfaces 12, 14 each preferablyinclude a plurality of anti-migration features designed to increase thefriction between the spinal fusion implant 10 and the adjacentcontacting surfaces of the vertebral bodies. Such anti-migrationfeatures may include ridges (or teeth) 24 provided along the top surface12 and/or bottom surface 14. The friction prohibits migration of theimplant 10 after insertion into the intervertebral space and during thepropagation of natural bony fusion. It should be appreciated by oneskilled in the art that such ridges (or teeth) 24 can be oriented in aparticular direction which will stabilize the implant in several degreesof rotation during placement.

The spinal fusion implant 10 of the present invention may also beprovided with one or more radiographic markers to allow for visualdetermination of proper implant placement. The radiographic markers maybe manufactured from any of a variety of suitable radiopaque materials,including but not limited to a metal, ceramic, and/or polymer material,preferably having radiopaque characteristics. The radiographic markersmay be provided in any size or shape suitable to facilitate effectiveand accurate visualization of implant placement.

The spinal fusion implant 10 include radiographic markers in the form ofelongated cylinders extending generally perpendicularly through theimplant 10 between the top and bottom surfaces 12, 14. Alternatively,radiographic markers may include a shorter element which extends onlypartially from either the top surface 12 or the bottom surface 14 (thatis, does not extend through the entire height of the implant 10). As afurther alternative, radiographic markers may extend at least partially(but not fully) toward either or both of top and bottom surfaces 12, 14(that is, radiographic markers may be disposed completely within thebody of the implant 10).

As best appreciated in FIGS. 7 and 10, the proximal end 20 of the spinalfusion implant 10 may be provided with at least one radiographic marker26 positioned extending at least partially through the implant betweentop and bottom surfaces 12, 14 near the intersection of second lateralside 18 and proximal surface 40. Radiographic marker 26 may preferablyindicate the position of the posterior-most portion of the implant 10.Spinal fusion implant 10 may include at least one radiographic markerpositioned at the intersection of the second lateral side 18 and thedistal end 22. Preferably, there are two markers positioned at thisintersection, a first radiographic marker 28 extending at leastpartially through the implant from the top surface 12 and radiographicmarker 30 extending at least partially through the implant from bottomsurface 14 to identify the tallest points of the spinal fusion implant10. The distal end 22 may be provided with radiographic marker 32comprising a unitary element fully extending between the top and bottomsurfaces 12, 14 at or near the intersection of distal end 22 and firstlateral side 16. Radiographic marker 32 may preferably indicate theposition of the anterior-most portion of the spinal fusion implant aswell as an indication of the anterior height of the implant. As will beshown in greater detail below, the orientation of radiographic markers26, 28, 30, 32 provide an indication of the oblique placement of thespinal fusion implant 10 and the direction of rotation that is needed tobring the implant 10 into the desired positioning.

The spinal fusion implant 10 includes a large aperture 34 extendingbetween top and bottom surfaces 12, 14. FIGS. 1-4 illustrate aperture 34extending in a vertical fashion between the top and bottom surfaces 12,14. The aperture 34 may be provided in any number of suitable shapes,including but not limited to generally circular, generally triangularand/or generally oblong (as shown by example in FIGS. 3 and 4). Thissingle aperture 34 is an additional feature for promoting fusion betweenthe upper and lower vertebral bodies which allow a boney bridge to formthrough the spinal fusion implant 10.

According to another further aspect of the present invention, thisfusion may be facilitated or augmented by including osteoinductivematerial(s) within the aperture 34 and/or adjacent to the spinal fusionimplant 10. Such osteoinductive materials may be introduced before,during, or after insertion of the spinal fusion implant 10 of thepresent invention, and may include (but are not necessarily limited to)autologous bone harvested from the patient receiving the spinal fusionimplant 10, bone allograft, bone xenograft, any number of non-boneimplants (e.g. ceramic, metallic, polymer), bone morphogenic protein,and bio-resorbable compositions, including but not limited to any of avariety of poly (D, L-lactide-co-glycolide) based polymers, such asthose disclosed in U.S. Pat. No. 6,013,853.

FIGS. 5-6 depict the spinal fusion implant 10 from side views. First andsecond lateral sides 16, 18 are generally parallel to one another (shownbest in FIGS. 3-4). The spinal fusion implant 10 may be further providedwith one or more lateral apertures 36 extending generallyperpendicularly therethrough from one lateral side 16 to the other 18.Lateral apertures 36 function to provide visualization at the time ofimplantation and at subsequent clinical evaluations. Lateral apertures36 may be provided in any of a variety of suitable shapes, including butnot limited to generally circular, generally triangular, generallyrectangular, and/or generally oblong (shown by example in FIG. 5-6), orany combination thereof. Although the spinal fusion implant 10 hereinincludes a pair of lateral apertures 36, the spinal fusion implant 10may include any number of lateral apertures 36 as desired.

Based on the generally radiolucent nature of the implant 10, the lateralapertures 36 provide the ability to visualize the interior of theimplant 10 during X-ray and/or other suitable imaging techniques whichare undertaken from the lateral (or “side”) perspective of the implant10. If fusion has taken place, the lateral apertures 36 will provide amethod for the surgeon to make follow up assessments as to the degree offusion without any visual interference from the spinal fusion implant10. Further, the lateral apertures 36 will provide an avenue forcellular migration to the exterior of the spinal fusion implant 10. Thusthe spinal fusion implant 10 will serve as additional scaffolding forbone fusion on the exterior of the spinal fusion implant 10.

The spinal fusion implant 10 further includes slots 38 extending fromproximal surface 40 along first and second lateral sides 16, 18. Slots38 are sized and dimensioned to interface with distal insertion tangs122 on insertion instrument 100 to provide steerability and torsionalsupport during insertion and insert-and-rotate maneuvers as will bedescribed in greater detail below.

FIG. 7 illustrates the proximal end 20 of the spinal fusion implant 10of the present invention. The proximal end 20 has a proximal surface 40that is tapered (angled) from the first lateral surface 16 to the secondlateral surface 18. This angular surface provides an advantage byallowing an oblique positioning of the spinal fusion implant 10 withinthe intervertebral space, without protruding into the spinal canal toavoid dural impingement after insertion.

Additionally, the tapered nature of the proximal surface 40 can aid inoverall fit of the spinal fusion implant 10 within the vertebral discspace. Significantly, the tapered proximal surface 40 on the proximalend 20 enables the spinal fusion implant 10 to maximize contact with theposterior portion of the cortical ring of each adjacent vertebral body.

The proximal end 20 may include a proximal engagement recess 46 whichextends inwardly in a generally perpendicular fashion relative to theproximal end 20. Although shown as having a generally semi-circularcross-section, it will be appreciated that the proximal engagementrecess 46 may be provided having any number of suitable shapes orcross-sections, including but not limited to circular or triangular.Furthermore, the proximal engagement recess 46 may extend fully or atleast partially along the length of the proximal surface 40. Proximalengagement recess 46 is dimensioned to receive and engage with aninsertion tool (described below) for inserting the spinal fusion implant10 into the intervertebral space.

According to the embodiment shown (by way of example only in FIGS. 7-9),the proximal engagement recess 46 is comprised of a keyed insertion slot48, a locking recess (undercut) 50, and a locking wall 52. Keyedinsertion slot 48 is complementary in shape to the rotational lock 128on the inner shaft 108. When the rotational lock 128 is inserted intothe keyed insertion slot 48, it falls into the locking recess 50 (orundercut) after it rotates and abuts locking wall 52, thereby lockingthe spinal fusion implant 10 with insertion instrument 100 andpreventing the implant 10 and insertion instrument 100 from movingrelative to one another.

FIG. 10 illustrates the distal end 22 of the spinal fusion implant 10 ofthe present invention. The distal end 22 has a conical (bullet-shaped)distal nose including a pair of first tapered (angled) surfaces 54 and apair of second tapered (angled) surfaces 56. First tapered surfaces 54extend between lateral surfaces 16, 18 and the distal end 22. Firsttapered surface 54 extending from second lateral surface/side 18 isgenerously curved between distal nose and lateral side 18 and functionsto distract the vertebrae adjacent to the target intervertebral spaceduring insertion of the spinal fusion implant 10. According to theembodiment shown, the distal end 22 is asymmetrically positionedrelative to the longitudinal axis of the implant. Specifically, thedistal end is preferentially curved (curved surface 44) towards thesecond lateral side 18. The asymmetric distal end 22 facilitatesinsertion while providing maximal surface area of the spinal fusionimplant 10. The asymmetric distal end 22 provides a gradual lead-intaper which protects nervous tissue in the spinal canal when placing thespinal fusion implant 10 into the disc space on its side and utilizingthe insert-and-rotate technique. Once implanted and rotated, theasymmetrical distal end 22 provides increased structural support byapproximating the anatomical shape of the anterior portion of thecortical ring of each adjacent vertebral body.

The top and bottom surfaces 12, 14 may be angled or tapered from distal(anterior end) 22 to proximal (posterior) end 20. According to anexample embodiment, in which the implant 10 has a variable heighttapering in a direction oblique to the length and width of the implant,as measured by the distance between the top and bottom surfaces 12, 14.Because the variable height of the implant tapers in a direction obliqueto the length of the implant, the height of the implant at the distalend 22 is greater than the height of the proximal end 20. Because thedirection in which the height of the implant tapers is also oblique tothe width of the implant, the height of the first lateral side 16differs from the height of the second lateral side 18 along at least aportion of the length of the implant. The practical result of thistapering along a direction oblique to the length and width of theimplant is that when the spinal fusion implant 10 is inserted obliquelywithin the disc space, the effective height correction occurs generallyparallel to the sagittal plane (i.e. anterior to posterior). Thisprovides for optimal restoration of the natural lordotic curvature ofthe lumbar spine. By way of example only, the oblique tapering of theimplant 10 height may occur at an angle measuring from 5 to 15 degrees.

The spinal fusion implant 10 preferably has variable rounds on opposingcorners of the implant 10 when looking at the implant along itslongitudinal axis. These opposing-corner variable rounds (shown here asRounds A and B) vary in their radius along the length of the implant. Inthe embodiment shown in FIGS. 11-12, Rounds A-B have a larger radius atthe distal end 22 and a smaller radius at the proximal end 20. Smallerrounds (shown here as Rounds C and D) have constant and equal radiialong the length of the spinal fusion implant. The radii at Rounds A andB are preferably approximately equal at any given cross-section alongthe entire length of the spinal fusion implant 10. These opposing-cornervariable rounds allow for more gradual lead-in at the distal end 22which facilitates insertion of the spinal fusion implant 10 duringinsert and rotate maneuvers.

The spinal fusion implant may be further provided with asymmetric convextop and bottom surfaces between first and second lateral sides toapproximate the anatomical concavities of the inferior endplate of thesuperior vertebra and the superior endplate of the inferior vertebra.According to one embodiment, the radius of curvature between first andsecond lateral sides 16, 18 is preferably smaller for the top surface 12than the bottom surface 14 the curvature of the top surface 12 will bedifferent at every cross-section along the length of the spinal fusionimplant 10 than the curvature of the bottom surface 14. It is well-knownthat vertebral body endplates generally have some degree of concavity,however the concavity of adjacent endplates within an intervertebraldisc space are rarely identical. The degree of convexity of the top andbottom surfaces 12, 14 between first and second lateral sides 16, 18 isnot identical to account for the asymmetrical concavity of the inferiorendplate of the superior vertebral body and the superior endplate of theinferior body. According to a preferred embodiment, the top surface 12has a larger degree of convexity between first and second lateral sides16, 18 than bottom surface 14.

It can be appreciated by one skilled in the art that the top and bottomsurfaces 12, 14 may be configured in any number of suitable shapes tobetter match the natural contours of the vertebral end plates. Forexample, top and bottom surfaces 12, 14 may be generally planar,generally concave, and/or generally convex. According to one or morepreferred embodiments, the top surface 12 of the spinal fusion implant10 is convex to approximate the concave of the inferior endplates of thesuperior vertebral body and the bottom surface 14 of the spinal fusionimplant is concave to approximate the concave surface of the superiorendplates of the inferior vertebral body. The degree of convexity of thetop and bottom surfaces 12, 14 along the length of the implant betweenproximal and distal ends 20, 22 is not identical to account for theasymmetrical concavity of the inferior endplate of the superiorvertebral body and the superior endplate of the inferior vertebral body.According to one or more preferred embodiments, the top surface 12 has agreater amount of convexity than bottom surface 14 along the length ofthe implant.

The spinal fusion implant 10 may be introduced into a spinal target sitethrough use of any of a variety of suitable surgical instruments havingthe capability to engage the implant. As described in FIGS. 13-16, thepresent invention includes an insertion instrument 100 for implantingthe spinal fusion implant 10. According to a broad aspect, the insertioninstrument includes a proximal connection region 102, a thumbwheel 104,an outer shaft 106, an inner shaft 108, and a distal insertion region110.

The proximal connection region 102 is sized and dimensioned forattaching and/or detaching a handle (not shown). The thumbwheel 104contains an inner aperture 112 for housing an interior spring (notshown) and a lock 114. Lock 114 resides at least partially withinthumbwheel 104 and includes an aperture 116 and is rotatable betweenlocked and unlocked positions via thumbwheel 104 as will be described ingreater detail below. Outer shaft 106 includes a proximal end 118extending distally from the thumbwheel 104, a central elongate bore 120carrying the inner shaft 108 therethrough, and distal insertion tangs122. Distal insertion tangs 122 engage with the slots 38 of the spinalfusion implant 10 via insertion slides 124 as will be explained ingreater detail below. The inner shaft 108 includes a distal region 128which terminates in a rotational locking mechanism. As shown in FIG. 15,according to one embodiment, rotational lock 128 includes a half-moonshaped key that is sized and dimensioned to fit into keyed insertionslot 48.

The insertion instrument 100 is attached to the spinal fusion implant 10by aligning the distal insertion tangs 122 with slots 38 on first andsecond lateral sides 16, 18. The implant may be attached to thepositioning insertion slides 1240 into the slots 38 until the distalinsertion tangs 122 are fully inserted within the spinal fusion implant10 and keyed rotational lock 128 is inserted into keyed insertion slot48 on the proximal end 20 of the spinal fusion implant 10. Pushing thespring-loaded thumbwheel 104 slightly and spinning it to the right movesthe lock from the unlocked position to the locked position. As thethumbwheel 104 moves, the rotational lock rotates 180 degrees and itfalls into the locking recess 50 (or undercut) and abuts locking wall52. Thus, the rotational lock 128 prevents the implant 10 from moving inan axial direction while the distal insertion tangs 122 preventtranslation in the medial/lateral and cranial/caudal directions therebylocking the spinal fusion implant 10 with insertion instrument 100 andpreventing the implant 10 and insertion instrument 100 from movingrelative to one another.

The spinal fusion implant 10 may be introduced into a spinal target sitehaving first been prepared through the use of one or more trialinstruments having the capability to size the spinal target site. Asdescribed in FIGS. 17-20, the present invention a trial instrument forselecting the proper size of spinal fusion implant 10 and determiningthe correct position of the spinal fusion implant 10 under fluoroscopyprior to insertion. The trial instrument 200 comprises a connectorportion 202, a shaft portion 204, and a trial head 206. The trial head206 has a size and shape of the spinal fusion implant 10 to be used. Thetrial head 200 has a series of windows 208, 210, 212 formed withinlateral sides 214. Each window 208, 210, 212 preferably extendsgenerally perpendicularly from one lateral side 214 of the trial head206 to the other.

The trial instrument 200 may be formed of any material that prevents thepassage of x-rays therethrough (e.g. titanium). Since the windows extendcompletely through the trial head 206, the x-rays are able to passthrough and both the size and shape of the windows 208, 210, 212 arediscernable under fluoroscopy. In the example shown here, the trial head206 is provided with three windows, however any number may be used. Byway of example, the trial head 206 has a proximal shaped window 208, adistal shaped window 210, and a central shaped window 212. The shapedwindows 208, 210, 212 are arranged linearly along the axis of the trialinserter 20. The central window 212 is shown as having a generallyrectangular shape, however other shapes are possible. The central window212 comprises an aperture having a longitudinal axis that isperpendicular to the longitudinal axis of the trial inserter 200. Theproximal and distal shaped windows are positioned on either side(proximal side and distal side, respectively) of the central window 212.By way of example, the proximal shaped window 208 has a generallytriangular shape and is arranged to “point” in a proximal direction. Thedistal shaped window 210 also has a generally triangular shape and isarranged to “point” in a distal direction. The proximal and distalshaped windows 208, 210 comprise apertures having co-planar non-parallellongitudinal axes.

When viewed from the correct side, the axes of the proximal and distalshaped windows 208, 210 are divergent from one another and the centralaxis. This allows for rapid visual determination of rotationalpositioning of the trial head 206, and also for immediate instruction onhow to correct improper positioning. The parallax distortion of thefluoroscopic image is minimal when the trial head 206 is centered withinthe image and therefore the x-rays travel within a directly parallelmanner. Because metal prevents the passage of x-rays, a window willappear smaller if it is not directly aligned with the direction of thex-rays. As a result, one window (e.g. the central shaped window 212) isan indicator of directly parallel alignment), one window (e.g. thedistal shaped window 208) is an indicator of “hyper-obliqueness” and onewindow (e.g. the proximal shaped window 210) is an indicator ofhypo-obliqueness.”

Because the user immediately knows whether the trial instrument 200 is“hyper-oblique” or “hypo-oblique”, he/she also immediately knows thedirection to move his/her hand to get the correct placement of the trialhead 206, thereby decreasing the need for trial inserter repositioningand localizing x-rays thus reducing x-ray fluoroscopic exposure for userand patient. By way of example, when a trial instrument 200 is inserteddirectly oblique (proper position), the proximal and distal shapedwindows 208, 210 will appear the same size under fluoroscopy. Howeverwhen one of the proximal and distal shaped windows 208, 210 is largerthan the other, the surgeon/user knows that the trial is not correctlypositioned. Pivoting the trial head 206 in the direction of the largerwindow, the desired position may be achieved. FIG. 19 is an example of a“hyper-oblique” trial head 206. In this instance, the distal shapedwindow 210 is larger than the proximal shaped window 208, indicatingsuboptimal positioning of the trial 200. Pivoting the trial 200 in thedirection of the distal shaped window 210 will bring the trial head 206into ideal trial positioning. FIG. 20 is an example of a “hypo-oblique”trial head 206. In this instance, the proximal shaped window 208 islarger than the distal shaped window 210, also indicating suboptimalpositioning in the trial 200. Pivoting the trial 200 in the direction ofthe proximal shaped window 208 will bring the trial head 206 into idealtrial positioning.

According to a broad aspect of the present invention, the spinal fusionimplant 10 is capable of being used in minimally invasive surgicalprocedures, needing only a relatively small operative corridor forinsertion. By way of example only, the spinal fusion implant 10 will nowbe described in relation to a transforaminal lumbar interbody fusion(TLIF) technique, in which the intervertebral disc space is approachedfrom a postero-lateral direction, however it should be understood thatthe spinal fusion implant 10 is capable of use in a variety of surgicalprocedures not described herein. After creation of this operativecorridor and preparing the disc space (using techniques commonly knownand used in the art), a trial inserter (e.g. the trial inserter of FIGS.17-20) may be used to select the proper size of the spinal fusionimplant 10.

The spinal fusion implant 10 is mated to an insertion device (e.g.insertion instrument 100) and advanced through the operative corridortoward the target intervertebral space. The spinal fusion implant 10 maybe oriented with the lateral sides 16, 18 facing in a caudad/cephaladdirection, for example with the first lateral side 16 facing a caudad(inferior) direction and the second lateral side 18 facing a cephalad(superior) direction. When the distal end 22 of the implant 10 reachesthe intervertebral disc space, each of the pair of first taperedsurfaces 54 will come into contact with one of the adjacent vertebralbodies. As the implant 10 is advanced into the intervertebral discspace, the pair of first tapered surfaces 54 will serve to distract thevertebral bodies, allowing the implant to fully enter the intervertebralspace.

Since the first and second lateral sides 16, 18 are preferably providedwith generally smooth surfaces, the spinal fusion implant 10 shouldadvance with relative ease into the disc space once the adjacentvertebral bodies have been distracted. Once the implant 10 has beenpositioned in its desired location, the user will then rotate theimplant 90° such that the top and bottom surfaces 12, 14 face in acaudad/cephalad direction and the anti-migration features 24 engage thevertebral bodies. Significantly, the direction of rotation is criticalto ensure proper placement of the implant 10 such that the edges of theproximal surface 40 rest on the cortical ring of the vertebral bodies,that the proximal surface 40 does not protrude into the spinal canal,and the implant 10 tapers in the appropriate direction (e.g. anterior toposterior rather than posterior to anterior). For example, if the spinalfusion implant 10 approaches a patient's spine posteriorly from theright with the (longer) first lateral side 16 facing caudally, thenimplant 10 must be rotated in a counter-clockwise direction to achieveproper positioning. Similarly, if the spinal fusion implant 10approaches a patient's spine posteriorly from the left side with the(longer) first lateral side 16 facing caudally, then implant 10 must berotated in a clockwise direction to achieve proper positioning.According to one embodiment the implant may include one or more markingsor other indicia to help facilitate the proper positioning. According toone embodiment (not shown), for example, the first lateral side 16 maybe marked with “lateral” to indicate that it should face to the exteriorof the disc space, and the second lateral side 17 may be marked with“medial” to indicate that it should face the interior of the disc spacewhen the implant 10 is rotated into position. Once the spinal fusionimplant 10 has been rotated into position, the insertion instrument 100may be detached and removed from the operative corridor.

In accordance with the present invention, the user is provided with oneor more methods to aid in verifying the desired positioning of thespinal fusion implant 10 using lateral fluoroscopy to localize internalvisualization markers and verify movement of the spinal fusion implant10 within the disc space. FIG. 21 A depicts a spinal fusion implant 10positioned in the intervertebral disc space, however not in the desiredoblique alignment. As illustrated in FIG. 21 B, radiographic markers 28,30 will appear spaced apart from radiographic marker 32 on lateralfluoroscopy. FIG. 22 A depicts a spinal fusion implant 10 positioned inthe intervertebral disc space, in the desired oblique alignment. Asillustrated in FIG. 22 B, radiographic markers 32 will appear to alignwith radiographic marker 32 on lateral fluoroscopy.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined herein.

What is claimed is:
 1. An implant comprising: a body having a topsurface and bottom surface, a first sidewall and a second sidewallopposing one another, the first sidewall having a first length and thesecond side wall having a second length, and a first end and a secondend, the first sidewall joining the upper surface at a first cornerextending along a length of the body a first corner length and joiningthe bottom surface at a second corner extending along a length of thebody a second corner length, the second sidewall joining the uppersurface at a third corner extending along a length of the body a thirdcorner length and joining the bottom surface at a fourth cornerextending along a length of the body a fourth corner length, each of thefirst, second, third, and fourth corners being rounded, the secondcorner having a second corner radius that is constant along the secondcorner length and the third corner having a third corner radius that isconstant along the third corner length, the first corner having a firstcorner radius that is variable along the first corner length and thefourth corner having a fourth corner radius that is variable along thefourth corner length.
 2. The implant of claim 1, wherein the secondcorner radius and third corner radius are equal to one another.
 3. Theimplant of claim 1, wherein the first corner radius and fourth cornerradius are equal to one another at opposing points along the firstcorner length and fourth corner length.
 4. The implant of claim 1,wherein the first corner radius and fourth corner radius decrease insize moving in a direction from the first end towards the second end. 5.The implant of claim 1, wherein the second corner radius and thirdcorner radius are equal to one another and the first corner radius andfourth corner radius decrease in size moving in a direction from thefirst end towards the second end and are equal to one another atopposing points along the first corner length and fourth corner length.6. The implant of claim 1, wherein the body has a variable heightbetween the upper surface and lower surface.
 7. The implant of claim 6,wherein the height of the body at the first end is greater than theheight of the body at the second and the height of the body along thefirst sidewall is greater than the height of the body along the secondsidewall.
 8. The implant of claim 6, wherein the height tapers in afirst direction oblique to a length of the body and in a seconddirection oblique to a width of the body/
 9. The implant of claim 1,wherein the first end of the implant includes a first pair of opposedtapered surfaces and a second pair of opposed tapered surfaces.
 10. Theimplant of claim 9, wherein the first pair of opposed surfaces andsecond pair of opposed surfaces all meet to form a conical nose.
 11. Theimplant of claim 10, wherein the conical nose is asymmetrically situatedabout a central longitudinal axis of the body.
 12. The implant of claim9, wherein one tapered surface of the first pair of tapered surfacestapers more than the other tapered surface of the first pair ofsurfaces.
 13. The implant of claim 1, wherein the second end of theimplant includes an engagement recess for mating with an insertioninstrument.
 14. The implant of claim 13, wherein the engagement recessincludes a keyed insertion slot.
 15. The implant of claim 14, whereinthe keyed insertion slot is asymmetric along at least one axis.
 16. Theimplant of claim 15, wherein the keyed insertion slot includes a lockingrecess and a locking wall.
 17. The implant of claim 1, wherein the bodyincludes four radiopaque markers.
 18. The implant of claim 17, whereinone of the four radiopaque markers is situated in the first end of theimplant and the other three radiopaque markers are situated in thesecond end of the implant.